525 Background: The hallmark of circulating tumor DNA (ctDNA) is its rapid turnaround and non-invasive nature. According to American Society of Clinical Oncology (ASCO) and College of American Pathologists joint ctDNA review published in March 2018, there is no sufficient evidence to support the use of ctDNA in practice for GI cancers. However, there were numerous studies presented at ASCO Annual Meeting supporting its value. We aimed to summarizing on its role in the management of gastrointestinal cancers based on the studies presented recently. Methods: We limited our search to keywords ‘ctDNA’, ‘circulating tumor DNA’, ‘cell-free DNA (cfDNA)’ and/or ‘liquid biopsy’, at the 2018 ASCO Annual Meeting library abstracts and presentations. Results: There were 35 studies that revolved around ctDNA as a diagnostic tool, prognostic marker and a measure of tumor heterogeneity in gastrointestinal cancers. Depending on the assay used, the results of several studies showed that ctDNA was able to identify relevant mutations including RAS, HER2/Neu, BRAF, MET, BRCA2, APC, TP53, ROS1, PTEN and NF1. The prognosis in terms of tumor mutation burden, objective response rate, metastasis and survival was also estimated based on ctDNA. The findings showed that higher baseline ctDNA levels and/or increased number of mutations detected in ctDNA were associated with poor survival and multi-site metastasis. Right-sided colon cancer was associated with higher number of mutations in ctDNA than left-sided colon and rectal cancers. Similarly, tubular adenocarcinoma subtype of gastric cancer was more likely to have higher ctDNA levels than signet-ring cell subtype. The response to therapy and the residual metastatic disease which was otherwise not detected on imaging could be detected by ctDNA as well. Conclusions: The research at ASCO 2018 report an increasingly promising role of ctDNA in many forms in patients with gastrointestinal malignancies. Experts at the meeting argued that this may well indeed be ready for prime time for certain GI malignancies including colorectal cancers. Prospective studies and studies showing its feasibility into practice can potentially help revise the current guidelines.
Role of Circulating Tumor DNA in Gastrointestinal Cancers: Update From Abstracts and Sessions at ASCO 2018
